Methamphetamine (METH) is an illicit drug commonly used (and abused) by HIV-infected patients. METH exacerbates HIV-related neurological impairments and brain injury. Clinical studies show that HIV and METH have additive effects on neuronal loss and glial activation compared to either HIV or METH insult alone. Recent findings also demonstrate that APOE4 suppress K+ channel activities while METH elicits bursts of action potentials. APOE4, a product of the APOE ?4 allele, is a risk factor for Alzheimer's Disease. The APOE ?4 allele is also implicated in accelerating the progression of HIV Disease. To date, no study has been conducted to investigate how APOE gene polymorphisms affect the nature of CNS injury in the presence of HIV infection and in combination with METH use. Our long-term goal is to elucidate the role of genetic variations and their effects on the brain in the presence f both HIV infection and the drugs commonly abused by these individuals. The objective of this proposed work is to better understand the interactions between APOE protein, HIV-Tat protein and METH in promoting neuronal injury via disruption of electrical and physiological responses. Our overall hypothesis is that differential expression of APOE isoforms will determine the severity of neural damage induced by HIV-Tat (during HIV infection) and by METH by directly influencing electrical activities and consequently affecting intracellular calcium (Ca2+) homeostasis. In Aim 1, we will characterize the DNA methylation patterns of post-mortem brain tissues of HIV+ and HIV + METH individuals who are carriers (?4+) and non-carriers of the APOE ?4 allele (?4-). We will determine how methamphetamine use changes the DNA methylation patterns of the APOE promoter and exon 4 CpG islands in HIV-individuals who are ?4+ and ?4-. In Aim 2, we will examine neuronal responses to Tat and METH in the presence of APOE3 and APOE4 proteins by monitoring neurons' electrical activities (Ca2+, Na+, and K+ currents and resting membrane potentials). To achieve this, we will measure macroscopic Ca2+, Na+, and K+ currents and membrane potentials changes using whole-cell patch clamp recordings (in voltage clamp and current clamp modes). These recordings will be done in different APOE isoform backgrounds with and without METH. The data from this research will form the basis of a future R01-level proposal for this New Investigator applicant who is at the early stage of her research career.